Minimal-loss flywheel battery and related elements

ABSTRACT

Electric power is stored in a flywheel assembly, from a dc power buss, and supplied to the buss, through electronics associated with a motor/generator, its rotor integral with a flywheel supported by magnetic bearings. The power is reciprocally converted by the motor/generator, controlled by current in its polyphase stator windings, between electricity and kinetic energy. The flywheel and rotor assembly spins around a vertical axis. The rotor contains radial-field permanent magnets attached to supporting outer annular high-permeability steel, attached to inner annular steel. This completes a path for the magnets&#39; field, which interacts with current in the stator windings, to produce torque between the rotor and the stator. Polyphase sinusoidal currents in the stator windings are controlled by the associated electronics, responsive to respective rotation angle sensors and the dc power buss voltage, with override control responsive to flywheel rotation speed, axial and radial position sensors, and operator settings. During normal operation, the flywheel assembly is levitated by axial attraction of its annular high-permeability poles near its top, to a fixed annular permanent magnet and high-permeability poles above it. The stator windings and non-rotating parts are affixed to a sealed and evacuated stationary flywheel enclosure. The flywheel assembly is released by mechanical backup bearings at startup, which then normally remain disengaged until shutdown. During normal operation, the flywheel assembly is levitated by the axial magnetic field, which also provides inherently stable centering. Axial position stability, and continuous axial position adjustment to seek and maintain axial position where force due to the permanent magnet is equal to levitated weight, is provided by a cooperative annular concentric coil whose current is controlled by an axial servo responsive to an axial position sensor. The coil adjusts strength of the magnetic field between the fixed and rotating poles, and thereby dynamically adjusts and stabilizes lift force. A coil current time-integral is combined with axial position feedback, so that average current is continuously adjusted to zero, by axial position adjustment. Radial electromagnets damp flywheel swirling at resonant vibration frequencies, stabilize its spin axis attitude at spin speeds too low for effective gyro stabilization, and constrain radial position during possible earth tremors. At normal spin rates, with the spin-axis at the rotor assembly center of mass, spin-axis verticality is stabilized by gyroscopics and leveled by gravity.

REFERENCES

Descriptions of flywheel batteries and their various related elementscan be found in U.S. Pat. Nos. 5,614,777 set forth by Bitterly et al;567,595, 5,708,312, 5,770,909, and 58,644,303 by Rosen et al; 3,860,300and 4,147,396 by Lyman; 3,791,704 and 4,088,379 by Perper; 5,627,419 byMiller; 4,910,449 by Hiyama et al: 5,760,510 by Nomura et al: 5,777,414by Conrad; 5,319,844 by Huang et al; 4,444,444 by Benedetti et al;5,844,339 by Schroeder et al; 5,495,221, 5,783,885, 5,847,480,5,861,690, and 5,883,499 by Post; 5,705,902 by Merritt et al; 5,044,944and 5,311,092 by Fisher; 5,107,151 and 5,677,605 by Cambier et al; and5,670,838 by Everton; plus 3,969,005, 3,989,324, 4,094,560, and4,141,607 by Traut; and 4,799,809 by Kuroiwa.

BACKGROUND OF THE INVENTION

This invention relates to electric power storage with minimal losses,through power interface electronics and electromechanical energyconversion, in the inertia of a spinning flywheel, and by reciprocalmeans, stored kinetic energy conversion to electric power. The variouscomponent elements of the invention include: A high-speedmotor/generator, with cooperative power electronics and magneticbearings, electronic feedback control servos to stabilize the magneticbearings, a vertical-axis flywheel, integral with the motor/generatorrotor and rotatable magnetic bearing elements, to store kinetic energy,a vacuum enclosure to reduce air drag, mechanical backup bearings thatare not engaged during normal service, and a stationary energy-absorbinginstallation site to safely house the flywheel and its enclosure.

Rechargeable electrochemical batteries are commonly used for storingon-site and portable electric power. Lead-acid types provide the highestenergy-to-cost and power-to-cost ratios. But they require frequentmaintenance, fail without warning, are very heavy, corrosive,deteriorate over time, consist of mostly hazardous materials withdisposal problems, and their lifetimes are limited to under ten years—far shorter if subjected to repeated charge/discharge cycles or notpromptly recharged after supplying power. These battery drawbacks havebeen a major obstacle to on-site solar and wind power installations. Toprovide power on demand, such installations require power storage thatis subjected to daily and highly variable charge/discharge cycles.

Flywheel power storage devices, and the various elements needed fortheir implementation, have been set forth in the prior art, with variouscombinations of elements developed as alternatives to electrochemicalbatteries. The term “flywheel battery” has been used for thesecombinations of elements related to the prior art, and is used herein byway of reference to the complete power storage and recovery system ofthis invention.

Flywheel batteries of the prior art can supply only short-term power,and their energy is typically dissipated in less than an hour, due tohigh idling losses. This energy loss, without supplying output power, isfar worse than self-discharge exhibited by electrochemical batteries.

Prior art magnetic bearings, for use in flywheel batteries, that employthermal, hysteresis, and eddy effects, for moving mechanical devices, toadjust physical positions of magnetic materials for stability control,confront serious stability and reliability problems. Others, usingsuperconductor techniques (conductor repulsion of moving magnets),confront high idling losses.

Magnetic bearings have also been described for flywheels that operate ina weightless space environment. They include, at opposing ends of aflywheel spindle, permanent magnets, and electronic servos to adjustmagnetic forces for virtually zero power axial positioning andstabilization. Their design is not suitable for use in a terrestrialenvironment, as they require opposing magnets far too large andexpensive for commercially viable flywheel batteries.

Typical prior art motor/generators, used in flywheel batteries, haveefficiency of about 90%, with a substantial part of their loss in corelaminations subjected to high frequency pulse width modulation.Moreover, idling loss due to iron cores magnetically cycled bypermanent-magnet spinning rotors, causes high self-discharge rates. Withsuch high power conversion and idling loss, excessive heat is generatedwithin the evacuated flywheel enclosure. This heat can cause a varietyof failure modes. It also can cause excessive maintenance requirements,which prevent practical and safe installation, of flywheel batteriesintended for stationary on-site use.

In the prior art, methods to reduce idling losses have included meansfor separating the rotor and stator during periods when no power isconverted. These methods confront greatly complicated mechanicalstructures, and inability to quickly respond when the flywheel batterysystem needs to supply power. As with motor/generators based uponinduced field machines (e.g., alternating current induction motors), orvarious machines having variably excited field windings, when fieldexcitation is removed to reduce idling loss, they cannot perform asgenerators unless connected to an external power source, such aselectrochemical batteries.

A type of motor/generator, known in the art as coreless (in that itsstator windings are not in core slots), has also been used in prior artflywheel batteries. They incur high eddy current loss in their statorwindings. Those with stepwise commutation also incur rotor hysteresisand eddy loss, when converting power. Rotor heat does not have aconductive path to the enclosure, in systems having contactless magneticbearings, so high internal temperatures may be incurred. These losses,incurred while converting power and when idling, have heretofore notbeen adequately investigated and explained, and have been mistakenlyattributed to skin effect.

Explosion hazard of spinning flywheels is a serious concern. Safetymeasures, that depend on the flywheel's vacuum enclosure to contain apossible exploding rim, add significant cost and weight, and are notalways effective. Almost all fiber-composite rim flywheel batteries spinat rim surface speeds above Mach 1. They are contained within evacuatedenclosures, to prevent high windage losses. Maintenance needs of priorart flywheels preclude the safe, low cost siting and installationmethods set forth in this invention.

In the prior art, idling loss has been largely due to friction inmechanical bearings, and to motor/generators and magnetic bearings thatmagnetically cycle iron as the rotor spins, causing substantialhysteresis and eddy losses. The prior art also includes manycombinations of magnetic bearings that are stabilized and assisted bymechanical bearings of various types. Some use a motor/generator havingstandard mechanical bearings, coupled to a flywheel by materials havingradial compliance to minimize vibration stresses.

Mechanical bearings of the prior art incur serious heating and wear,running in vacuum at sustained high speed. Very high operatingtemperatures of critical parts, has been caused by high localized heatgeneration compounded by low heat transfer, further compounded bylubrication loss accelerated by lubricant boil-off in vacuum. Theseconditions have resulted in early mechanical bearing wear,deterioration, and high failure rates.

Vacuum loss in the prior art necessitates relatively frequentmaintenance to keep windage loss at acceptably low levels. Hightemperatures cause lubricants to boil and some composite fiber flywheelresins to outgas into a relatively small evacuated enclosed space. Inthe prior art, the enclosed space has been small, to minimize size andweight of the enclosure, which has thick walls designed to contain apossible exploding flywheel rim. A small enclosure space, with highinternal temperatures and materials that outgas, does not reliablymaintain a vacuum.

At high temperature, even coercive force of permanent magnets isreduced. This has required more adjustment of magnetic bearings, imposedhigher loads on mechanical bearings, and caused reduced torque vs.current of motor/generators, with reduced back-emf vs. rotational speed.

BRIEF SUMMARY OF THE INVENTION

Flywheel power storage systems that are not subject to theaforementioned drawbacks and limitations would afford significantimprovement to numerous useful applications. These includeuninterruptible power supplies (UPS) to sustain critical electric powerfunctions (during power outages), in buildings commonly served by acentral power grid, and UPS plus power storage for on-site distributedsolar and wind power systems.

Therefore, general objectives of this invention are to provide improvedlong-life flywheel batteries, for stationary installations, without thepower losses, internal heating, vacuum loss, maintenance, explosionhazard, high cost, and malfunctions of the prior art; plus improvementsto related elements needed for the flywheel batteries.

A primary and specific objective is to provide a flywheel battery havinga motor/generator with no magnetic hysteresis and minimal eddy currentlosses, and with mechanical bearings used only as temporary backup; itsrotor integral with magnetic bearings that need virtually nosteady-state power to drive their axial and radial position stabilizingelectromagnets, that also do not incur magnetic hysteresis and eddycurrent losses, and that can use low-cost magnets.

Another specific objective of this invention is to provideelectromechanical power conversion at greater efficiency, with lessidling loss, by the flywheel battery motor/generator. This alsominimizes stator winding heating, resulting thermal stresses, andpossible outgassing of resin molding, and provides maximum overallenergy storage efficiency.

Another objective of this invention is to especially minimize losses andconsequent heat in all flywheel parts which spin in the vacuum enclosurewithout physical contact and thermal conduction paths to any stationaryparts that can transfer heat out of the enclosure, to minimize thermalstresses and composite fiber flywheel resin outgassing.

Another objective is to eliminate need for lubricants in mechanicalbackup bearings, to remove a cause of vacuum loss, frequent maintenance,and mechanical bearing failures.

Another objective is to maintain all electronic components, and criticalregions therein, at cool temperatures, with minimal temperature cycling;also to provide low cost rotor angle and axial and radial positionsensors and circuits with good signal integrity that is substantiallyfree of ground loops, extraneous pickup, and cross-talk and further toprovide over-current and over-voltage protection for the electroniccomponents.

Another objective, consistent with and dependent upon the previousobjectives, is to provide a flywheel battery that does not requiremaintenance over a very long service lifetime; to reduce maintenancecost and especially to reduce need for access to the flywheel and itsvacuum enclosure, so as to facilitate housing the flywheel in a sitecapable of absorbing any possible explosive blast, in the possible eventof a flywheel rim disintegration, to protect people in and around thebuilding served, and prevent damage to the building, from a flywheelexplosion.

Another objective of this invention is to detect possible flywheel rimdeterioration or seismic shaking, by resulting flywheel axial and radialvibration, and begin a controlled flywheel slowdown and spindle captureby backup mechanical bearings, to minimize flywheel damage and preventexplosion, from possible rim disintegration or electronic controlmalfunction.

Yet another objective, consistent with and dependent upon the previousobjectives, is to produce a low cost and low weight vacuum enclosure forthe flywheel, with more interior vacuum space than in the prior art, tomaintain vacuum longer, without maintenance, and to enable safe flywheeloperation, installed and housed in a stationary site as describedherein.

Accordingly, a flywheel battery system and its component elements areherein described, which achieve these objectives, plus other advantagesand enhancements. These improvements to the art will be apparent fromthe following description of the invention when considered inconjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates a simplified block diagram of the flywheel battery,connected to store power from, and supply power to, a dc power buss.

FIG. 2 illustrates a cross-sectional view through the spin-axis, of theflywheel, magnetic bearings, motor/generator, backup mechanicalbearings, and stationary vacuum enclosure.

FIG. 3 illustrates an axial cross-sectional view of the motor/generator.

FIG. 3a illustrates an enlarged cross-sectional view of a statorconductor segment, to show a typical eddy current path in the conductor.

FIG. 4 illustrates motor/generator electronics which control currentthrough a corresponding stator winding, and a simplified representationof its insulated strands.

FIG. 4a illustrates main paths for the magnetic field of themotor/generator.

FIG. 5 illustrates a preferred embodiment of a servo loop to stabilizeaxial levitation.

FIG. 6 illustrates one of a plurality of servo loops to control flywheelradial excursions.

FIG. 7 illustrates a cross-sectional view through the spin axis of arolling contact bearing having rolling separators.

FIG. 8 illustrates an axial cross-sectional view through the rollingcontact bearing.

FIG. 9 illustrates an axial cross-sectional view through the lowerradial electromagnets.

FIG. 10 illustrates a partial cross-sectional view in a plane throughthe spin-axis and through two lower radial electromagnets.

FIG. 11 illustrates a partial cross-sectional view through the spin-axisand through an alternate embodiment of the axial levitation magnetics.

FIG. 12 illustrates capacitive axial and radial position sensors for arotor assembly including conductive rings having low stray capacitanceattached to insulated sections.

FIG. 13 illustrates one embodiment of magnetic axial and radial positionsensors for a rotor assembly having high-magnetic-permeability sections.

FIG. 14 illustrates an alternate embodiment of magnetic axial and radialposition sensors for a rotor assembly having high-magnetic-permeabilitysections.

DETAILED DESCRIPTION OF THE INVENTION

The flywheel battery system is herein described in relation to itsgeneral use for storing on-site electric power in a stationaryinstallation, by way of reference to FIG. 1, followed by detaileddescriptions of its component elements and general variations.

FIG. 1 illustrates a block diagram of a preferred embodiment of theflywheel battery system according to this invention. Most of thesystem's electronics is housed in enclosure 1, which interfaces with adc power buss through respective positive and negative power terminals 4and 5. Power and feedback signal conduit 3 connects to respective powerand signal processing circuits in enclosure 1, and through a hermeticfeed-through 6 in flywheel enclosure 2, to corresponding statorwindings, electromagnet coils, and flywheel position sensors therein.

A preferred embodiment of this invention will include a conventionalcircuit breaker having a solenoid actuator with considerable inductance,connected in series between the electronics and the dc power buss. Thecircuit breaker will disconnect the flywheel battery from the power bussin the event of current overload or line short, thereby preserving allflywheel battery functions and stored energy. Circuit breaker inductancehelps to reduce current spikes that could otherwise damage powersemiconductors. When the fault causing the circuit breaker to open iscorrected, and the circuit breaker re-closed, the flywheel battery willresume normal service.

All electronic circuits will be designed to operate over the fullvoltage range of the dc power buss. But voltage spikes may be injectedonto the buss from a lightning strike, or from a power grid thatsupplies the buss. Such spikes are usually very short duration(typically microseconds), and do no circuit damage if buss voltage isclamped. In generator mode, the motor/generator control electronicsincludes voltage feedback plus over-voltage protection, so that it willnot inject current onto the buss that can result in buss over-voltage.Electronic circuit and dc buss over-voltage will be prevented withsub-nanosecond response, by a transient voltage suppresser (TVS),similar to a large junction area zener diode. Current through the TVSwill be sensed, to directly inhibit and turn off power semiconductorswith sub-microsecond response, to prevent the electronics from injectingmore current (supplied by the motor/generator) onto the buss. Also,negative voltage feedback to the electronics, from the dc power buss,normally limits current supplied to the buss from the electronics bymeans of a slower feedback loop, so buss voltage is prevented fromrising above prescribed levels by two redundant means.

FIG. 2 illustrates a cross-sectional view in a plane through the centerof stationary vacuum enclosure 2, the flywheel spin axis, themotor/generator, the magnetic bearings, and the backup mechanicalbearings. Scale is not exact, in order to show and identify essentialparts.

Essentially sinusoidal polyphase current through the motor/generatorstator windings 7 is conducted through hermetic feed-through 6,controlled by power stages of the electronics in enclosure 1. Themotor/generator control electronics is responsive to substantiallysinusoidal feedback signals from rotation angle sensors, throughfeedback conductors typified by 12.

This electronics is also responsive to the dc power buss voltage, rotorspin speed, an axial position signal, and to signals from a plurality ofradial position sensors at the top 22 and bottom 24 of the rotorspindle, which can override other input variables to prevent flywheeldamage in the event of abnormal vibration due to flywheel rimdisintegration or earthquakes.

The motor/generator rotor produces a radial pattern magnetic fieldhaving two or more poles (of even number) and magnetic intensity thatvaries as an approximate sinusoid with rotation angle, in the regionbetween radially magnetized permanent magnets 8 and 9 having respectiveopposite polarities and high-permeability inner steel core 11. Thismagnetic field interacts with a magnetic field produced by current instator winding 7 (and 71, which is shown in FIG. 3).

Flux from this field continues through return paths provided byhigh-permeability steel core 10, which also physically contains andsupports magnets 8 and 9 against high centrifugal forces that accompanyhigh speed rotation. Non-magnetic annular top shoulder 13 constrains therotor magnets at their top sides, and provides co-rotating attachmentfor a high-permeability spindle extension 23, and for ahigh-permeability ring (shown in FIG. 2) that provides an inner closedmagnetic path plus electromagnetic shielding from stator current forrotation angle sensor 12.

Linear Hall-effect sensors or, alternatively, magnetoresistorsconstitute the preferred embodiment for each of at least two rotationangle sensors. Magnetic sensors, such as these, can sense a loweramplitude replica of the magnetic field at the stator windings, providedby the rotor magnets through 13 and a relatively long gap. The sensorsprovide feedback signals which vary sinusoidally in synchronism withback-emf from a stator winding having corresponding phase. Back-emf peakamplitude is proportional to speed. Feedback signals from the sensorsvary sinusoidally with position only (with peak amplitude independent ofspeed).

The high-permeability ring shown in FIG. 2 is attached to 13. ItProvides a closed path for the rotor field through magnetic sensor 12,outside the stator windings. And it provides magnetic shielding forthese sensors, from stray magnetic fields caused by stator windingcurrents. It also minimizes flux cycling of stator iron near it, fromthe rotor field.

Lower shoulder 14 is attached to annular steel 10. It supports the rotormagnets at their bottom sides, provides attachment to co-rotating innercore 11, and supports co-rotating flywheel rim 15. The flywheel rimpreferably consists of concentric fiber composite cylinders, with anelastomeric resin bond between each cylinder. To minimize cost, thecylinder capable of the highest working tensile stress would have thelargest diameter, and lower cost (albeit lower strength) cylinders wouldbe used for successively smaller diameters. Flywheel rim 15 innerdiameter may be bonded to annular steel 10 by an elastomeric resin.

Co-rotating high-permeability steels (mainly 10 and 11) complete themagnetic paths for the rotating magnets of the present invention. Thefield resulting from polyphase sinusoidal stator current rotates insynchronization with the rotor. So rotor steel and magnets do not incurmagnetic cycling. Their hysteresis and eddy losses are thus virtuallyzero. In contrast, much of the prior art contains rotating andnon-rotating magnets and magnetic materials in alternating or highlyvariable fields, so as to incur magnetic cycling and resultant highhysteresis loss. Prior art permanent-magnet rotor motors, havinglaminated iron salient pole stator cores, are one example. Magnets andelectromagnets of magnetic bearings, which levitate high-permeabilitycylinders rotating around horizontal axes in particular, provide anotherexample of such lossy prior art.

This motor/generator embodiment is a high-speed adaptation based uponprinciples of the general and the coreless axial-field regenerativeservo motors set forth in my U.S. Pat. Nos. 4,085,355 and 4,520,300.Eddy current blocking and bucking methods set forth hereinbelow, withreference to FIG. 3, FIG. 3a, and FIG. 4, can significantly reducedominant idling losses, due to eddy currents in stator windings of allcoreless motors and motor/generators.

The motor/generator set forth herein has improvements and enhancementsto achieve virtually zero magnetic hysteresis losses, becauseessentially no high-permeability steel and no magnets are subjected tocontinuous magnetic flux cycling nor to magnetic flux variation, due torotor spin or interaction with stator current.

With reference to FIG. 2, the rotatable rotor assembly, attached to itsvertical-axis spindle and to flywheel rim 15, is axially levitated byattraction forces between concentric high permeability steel poles atthe upper end of rotating member 10, the lower side of non-rotating,annular, axially-magnetized, permanent-magnet ring 16, and the lowerside of non-rotating, high-permeability, annular steel 17, affixed toenclosure 2 by support member 19. Concentric coil 18 is providedbi-directional drive current, by its associated axial servo electronics,responsive to an axial position sensor, to stabilize the axiallevitation. These cooperative elements comprise the axial component ofcontactless magnetic bearings. They also provide inherently stablecentering forces, due to the same magnetic field that provides axiallevitation. The pole shapes shown here provide higher centering forces,compared to pole shapes shown in the prior art.

This magnetic levitation configuration has features to achieve virtuallyzero hysteresis losses, because no iron and no high-permeability steeland no magnets are subjected to continuous magnetic flux cycling, nor tosubstantial magnetic flux variation, due to rotor spin.

Also, all magnetic paths are effectively closed by high permeabilitymaterials, except in the pole gaps producing the required magneticforces. This minimizes stray magnetic flux and maximizes requiredmagnetic forces from permanent magnets and electromagnets. By using thefull flux density capability of high-permeability steel, it alsominimizes size and weight of steel poles near the top of the rotorassembly.

Another embodiment of the axial levitation magnetics is illustrated byFIG. 11, a partial cross-sectional view in a plane through the spinaxis. It has features to better accommodate a low-cost fixed ceramicmagnet 16. It mainly differs from the embodiment of FIG. 2 by theaddition of a fixed high-permeability annular pole 17 a, which withfixed annular pole 17 concentrates the magnetic field of the levitationpoles. In FIG. 11, the main flux path, for permanent magnet 16 andcurrent in coil 18, is denoted by the wide dashed lines through 16, 17,the inner pole gap, rotatable pole 10, the outer gap, and 17 a.

Except for stray flux, magnetic flux density through 16, 17, and 10 inFIG. 2, and through 16, 17, 10, and 17 a in FIG. 11, is inverselyproportional to the respective cross-sectional areas of these materials.For example, if pole widths of 17 and 17 a are equal, and if thediameter of 17 a is double that of 17, then 17 a will have an annularpole area, along with respective gaps to the poles of 10, approximatelydouble that of 17. So flux density at 17 would be approximately doublethat at 17 a. Likewise, if width of magnet 16 is double that at the poleof 17 a and its adjacent pole 10, then flux density at the gap of 17 aand 10 will be approximately double that at magnet 16. This is realizedonly with very small pole gaps, because stray flux increasesconsiderably as pole gaps increase. To achieve zero steady-state currentin coil 18, axial pole gap needs to be selected so that it isproportional mainly to parameter variations of magnet 16.

Magnet 16 is preferably a ceramic ferrite, having a flux density of 4000gauss at zero oersted. Steel pole materials have arbitrarily highpermeability at flux densities to 16000 gauss, each have widths (i.e.,outer minus inner radius) approximately half that of the magnet, and, tofacilitate this explanation, flux paths through the pole gaps are firstconsidered to be infinitesimally short. Then distinct features of theaxial levitation can be seen from this example:

Because magnetic forces of attraction are proportional to flux densitysquared, and to pole area, poles which concentrate flux into half asmuch area can approximately double the force of attraction between them.Flux density at 17 a will be approximately 8000 gauss, for this example.And flux density at 17 will be 16000 gauss. So the axial force between10 and 17 would be approximately double that between 10 and 17 a. Forceexerted between cooperating poles having a smaller diameter helps toreduce need for servo control of tilt instability.

Relatively thin annular poles, between 10 and 17, having width equal tothe pole between 10 and 17 a, enable a higher centering force gradient,for the inherently stable centering that they provide. With increasingdistance between the fixed and rotatable poles, stray flux increases;and flux density in magnet 16 may decrease to 3000 gauss, with 5000gauss in the gap between poles 17 a and 10, and 7500 gauss in the polesbetween 17 and 10. Accordingly, levitation pole gaps will be small,consistent with dimensional and magnet property tolerances.

Pole 17 a (along with the other cooperative steel poles) provides a poleface that can be very precise and have consistent high-permeability. Soany chips, cracks, or defects of magnet 16 do not cause flux variationin the levitation pole materials or the magnet, with rotor spinning.Also pole 17 a, after it is installed, protects magnet 16 from damageduring subsequent assembly and test procedures. Ceramic ferrite magnetsare low cost, but have relatively low strength. Chips and cracks areinevitable. Only their flat surfaces are normally ground and relativelyprecise, but may have cracks. With pole 17 a in combination with pole17, as shown in this invention, possible point-to-point variations inproperties of magnet 16, and irregularities of its annular surfaces,will not degrade levitation performance or cause hysteresis or eddylosses.

A plurality of radial electromagnets at the top of the rotor spindle,represented by coil 20 and high-permeability steel cylinder 21, affixedto the flywheel enclosure, are juxtaposed around annular rotor steel 23,to produce attractive radial forces at the top of the rotor assembly.Servo control, for this upper electromagnet and the one diametricallyopposite it, is responsive to upper radial sensor pair 22.

A minimum number of electromagnets, at respective upper and lowerlocations, is three, placed 120° apart. The minimum number of sensors,with three electromagnets, is two, which would require signal processingto produce a third feedback signal derived from the two sensor signals.A preferred embodiment of the invention has four electromagnets, atrespective upper and lower axial positions, 90° apart, and two pairs ofdiametrically opposed sensors, aligned with the electromagnets, 90°apart. One pair of sensors provides radial position feedback for servoelectronics controlling the pair of electromagnets aligned with thatsensor pair. The other sensor pair provides feedback to control theelectromagnet pair aligned with it.

An identical set of electromagnets, to produce controlled radial forcesat the bottom of the rotor assembly, is represented by electromagnetcoils 80 and 80 _(o) and iron 81 and 81 _(o) affixed to the enclosure,and rotor steel 11. A cross-sectional view, in a plane perpendicular tothe spin axis, and through the center of these lower radialelectromagnets, is illustrated in FIG. 9. A partial cross-sectional viewthrough the spin-axis is illustrated in FIG. 10, which also illustratesthe main flux path through the poles 81 _(o) of the radial electromagnetdiametrically opposite 81.

The flux path is shown as a wide dashed line, which loops through theelectromagnet's core and an annular section of inner rotor core 11.Servo control, for the two diametrically opposed radial electromagnetsshown, is responsive to lower radial sensor pair 24 (shown in FIG. 2).

The upper and lower electromagnets provide radial vibration damping andradial position stiffening, to limit rotor assembly swirling and todampen radial vibration due to production tolerance eccentricities atresonant frequencies. They also limit radial excursions at spin ratestoo low for effective gyroscopic stabilization of the spin axis, andconstrain relative radial motion between rotating and fixed elementsduring possible earthquakes.

Radial electromagnet iron 21 is affixed to the enclosure by supportingmember 19. Radial electromagnet iron 80 is likewise affixed to theenclosure by supporting member 30.

Practitioners of this art will recognize that the radial electromagnetsdescribed above, to exert force, require power to drive their respectivecoils, and that they subject their cooperating cylindricalhigh-permeability rotor sections to magnetic cycling when the rotorspins.

Each of the two rotor sections (one at the top and one at the bottom ofthe rotor assembly) are subjected to flux density that cycles betweenzero and the maximums needed to produce radial forces required tomaintain prescribed radial position. The magnetic flux path, movingrelative to the rotor steel as it spins, is illustrated by wide dashedlines in FIG. 10.

To minimize this power loss and resultant heating, this inventionincludes the following improvements over the prior art:

The vertical flywheel spin axis of this invention does not requireradial forces to support the flywheel against radial gravitationalforces, as do flywheels with horizontal spin axes.

In prior art, flywheels having horizontal spin axes are supported by acombination of permanent magnets and stabilizing electromagnets, withopposite poles orientated along the same cylindrical steel rotor section(i.e., rotated in place, to 90° from the electromagnets of thisinvention). They incur heavy continuous losses, to levitate spinningrotors.

Also, the radial electromagnets' moving magnetic path, on rotor sectionsof this prior art, is essential radially inward, to circumferential, toradially outward, and completing its closed magnetic path. Radial pathsin the rotor, of this prior art, incur continuous magnetic cyclingbetween plus and minus the maximum flux levels required to produceforces to support the spinning flywheel weight. At equivalent forcelevels to those produced by radial electromagnets of this invention,this prior art could sustain continuous hysteresis losses in rotorsteel, due to rotor spin, amounting to roughly double or more, of thepeak, and only temporary, hysteresis losses sustained by the rotor steelaccording to this invention.

Moreover, servos controlling the radial electromagnets of the presentinvention have a prescribed zero-crossover dead-band, so they will notproduce restoring forces unless radial speed or displacement exceedsdesign tolerance levels. Therefore, they are energized only rarely, andremain inactive during normal operation of this flywheel battery.Average power to drive them, and consequent magnetic hysteresis and eddylosses, are thus virtually zero.

The vertical spin-axis and improved method of rotor levitation,stabilization, and stiffening of its axial and radial position, providedby this invention, will have the following described additional benefitsover the prior art:

Axial levitation forces, that provide lift forces acting only at the topof the rotor assembly, combined with downward gravitational forces on arotor assembly having a low center-of-gravity, produce a leveling torquethat can maintain spin-axis verticality within one degree or so,relative to level non-rotating elements of the flywheel. This levelingtorque is very useful, in that it counteracts precession torque due toearth rotation. A low center-of-gravity helps, because even a fewdegrees of tilt will cause magnetic fluctuation and resulting hysteresislosses in the annular materials of the axial levitation magnetics.

The rotor assembly, spinning at very low speed, may tilt and wobble, dueto even slightly unbalanced rotor assembly mass distribution and axialmagnetic lift forces. Small diameter axial lift magnetic poles, and arotor assembly having a low center of gravity, alleviate such tilt. Theradial electromagnets stabilize it whenever needed.

At low spin speed, the radial electromagnets may need to occasionallyexert radial forces, to maintain spin-axis centering and verticalitywithin a selected dead-band tolerance of the servos controlling them.However, at spin speeds above about 10% or so of maximum, gyroscopiceffects will stabilize the flywheel against spin-axis wobble. So theradial electromagnets are needed to control spin axis verticality atvery low spin speeds, such as during rare power-up and power-down, butneed not be energized during normal operation.

Flywheel spin speed at 10% of maximum corresponds to 1% of maximumenergy storage. However, at 10% of full speed, back-emf is 10% ofmaximum; and mainly due to current limits of the power electronics,charging and discharging power is limited to 10% of the power at fullspeed, unless current is boosted by a factor of ten. This would requirevery expensive power electronics, and reduce motor/generator efficiencyconsiderably. So the preferred embodiment will operate between about 40%and 100% of full speed, corresponding to about 20% and 100% of fullenergy capacity. With lower speed restricted to 40% of maximum, powerelectronics can be rated to conduct current with at least a 40% designmargin at 40% of maximum speed and 100% at maximum; and the flywheelwould be oversized about 20% to provide full rated energy output when itis decelerated from full speed to 40% of full speed.

A mechanical backup bearing 23 a at the top of the rotor spindle, and 25a at the bottom, engaged by contact at beveled backup bearing touchdownsurfaces 23 and 25 with mating contact surfaces on the rotor assembly,will be engaged during flywheel battery storage, transit, andinstallation procedures. Beveled surfaces 23 and 25 restrict both axialand radial excursions.

Backup bearings may also be engaged, by mechanisms like 27, to preventinternal flywheel damage, in the event that electronic control of themagnetic bearings is lost, due to accidental in-service disconnection orelectronic component failure.

The bottom backup bearing is engaged and disengaged by gearing driven bya small electric motor 26. Parts of the bottom backup bearing, which donot spin with the rotor, are affixed to the enclosure by support member30. Similar parts at the top are affixed to the enclosure by supportmember 29. The top backup bearing is engaged and disengaged by gearingmechanism 27, driven by a small electric motor 28.

To protect the flywheel in the event of electronics malfunction, apreferred embodiment of this invention will provide in the flywheelenclosure a large capacitance, supplied through a rectifier, to storepower for driving motors such as 26 and 28.

Any possible electronics malfunction or disconnect can be configured torelease a trigger to a device such as a silicon controlled rectifier, todrive both motors into the fail-safe engaged positions of the backupbearings.

Motor 28 and the mechanism it drives, for engaging and disengaging thetop backup bearing, is not needed in embodiments wherein the outer raceof the top backup bearing is affixed to the enclosure. For theseembodiments, to activate backup, motor 26 will drive the backup bearingup to the flywheel rotor assembly, until it first engages the bottomcontact surfaces, and then further up until the top contact surfaces areengaged.

Ratio of rotor length to flywheel diameter in the preferred embodimentof this invention is higher than the proportions illustrated in FIG. 2,for various reasons: The ratio of active to return wire in themotor/generator can be higher, for greater power conversion efficiency.Signal disturbance to position sensors, from permanent magnets andactuator coils can be reduced, by increasing distance therebetween. Alower center-of-gravity helps to stabilize verticality of the spin axis.Eddy current bucking and blocking methods set forth herein are alsofacilitated.

In FIG. 2, part sizes are proportioned so that essential components inthe flywheel enclosure are therein visible, and so that adequate spaceis available for numbered component designators. So, to facilitate aclear description of this invention, parts are not necessarily drawn toaccurate scale. For example, inner rotor pole 11, to resist bending (dueto mass eccentricity relative to the spin axis) at high spin speed,preferably has larger inside and outside diameters, with greater wallthickness, compared to proportions in FIG. 2. This reduces stress at itsshoulder, where it is attached to annular support 14, and reduces itsflux density. Stator 7, rotor magnets 8 and 9, and outer steel cylinder10, also have preferably larger diameters, to accommodate a largerdiameter inner rotor pole. But the upper levitation poles of 10 havesmaller diameters, so they can withstand centrifugal forces at high spinspeed, and do not cause undue tilt instability.

Motor/generator improvements provided by this invention are set forthbelow by way of reference to FIG. 3, FIG. 3a, FIG. 4, and FIG. 4a (whichshows the rotor magnetic field paths).

FIG. 3 and FIG. 4a show axial views of cross-sections of a 2-pole2-phase embodiment of the radial-field motor/generator set forth in thisinvention. Stator winding 7 is shown in these views, in fixed relationto the second phase winding 71. For this 2-phase embodiment of theinvention, shown by way of example, winding 71 is positioned 90° fromwinding 7.

A 4-phase embodiment of the motor/generator would have an additional twostator windings, displaced 45% from windings 7 and 71. Rotor anglesignals and corresponding current control electronics, plus connectiontherebetween, for two additional phases, would need to be added. Astraightforward addition of two more sensors, corresponding electronics,and cabling, would also be needed, or additional feedback signals can bederived by combination, as explained next:

If the minimum two angle sensors (represented by 12 in FIG. 2) providegood sinusoidal vs. rotor angle approximations, a plurality ofsinusoidal signals vs. rotor angle for additional phases can be derivedby combining them. For example, rotor angle signals needed for thepreferred 4-phase embodiment are respective sum and difference of thefirst two signals scaled by 70.7% (multiplied by 0.707). For a 3-phaseembodiment, the two sensors represented by 12 need to be disposed 120°apart. The 3_(rd) phase angle signal would then be the negative value oftheir sum.

Having only 2 poles, but 3 or more phases, would reduce eddy loss in thestator windings, in comparison to maximum motor/generator power, becauseit results in a smaller flux density gradient over the width of thestator windings. More phases permits smaller diameter stator windings,for the same power handling capability, due to fuller use of statorspace. That results in more efficient phasor addition of back-emf andtorque from multi-turn windings (which would span a smaller rotorangle), and relatively less eddy losses. These benefits will beexplained by the simplified analysis of eddy losses, by way of example,which follows hereinbelow:

Currents through these respective windings, and back-emf across theirterminals, have approximately sinusoidal waveforms having 90° relativetime phases. Permanent magnets 8 and 9 have radial fields, one withinward polarity and the other outward. In one embodiment, these magnetsare tapered symmetrically along their axial direction so their axialdimensions are less at their nearest approach to each other and maximumat their centers. In another, magnets 8 and 9 are preferablyneodymium-iron-boron, and magnets 8 a and 8 e, along with 9 a and 9 e,are preferably ceramic ferrites supporting about half the flux densityfor the same thickness.

Both flux shaping methods result in magnetic flux, at the stator 7 andat the rotation sensor 12, that closely approximates a sinusoid, as afunction of rotation angle. The resulting magnetic field followssymmetric closed paths through the magnets, the stator winding region,inner high permeability material 11, and outer high permeabilitymaterial 10.

All elements shown in FIG. 3, except the stator windings, are part ofthe motor/generator rotor. When the rotor spins, for a moment when it isat the position illustrated, momentary back-emf across terminals 7 c and7 e of winding 7 (shown in FIG. 4) is at a maximum, while back-emfacross the terminals of winding 71 is at zero. The magnetic field fromthe rotor magnets rotates with the rotor. Its main paths, through therotor and stator, are shown by wide dashed lines in a cross-sectionalview perpendicular to the spin-axis, illustrated by FIG. 4a.

This type of motor, known in the art as coreless, is characterized bytwo significant differences from conventional salient-pole motors:

Its stator windings have very low inductance. This requires seriesinductors 31 and 32, shown in FIG. 4, for stator current control bypulse width modulation (PWM).

H-bridge 34, shown in FIG. 4, provides drive current control at onepolarity by switching Q1 at a PWM frequency generally below 100 kHzwhile Q3 is ON. And it provides drive current control at the oppositepolarity by switching Q2 at PWM frequency while Q4 is ON. Diode D4provides free-wheeling in the first case, and D3 in the second. Thisoperating mode accelerates the flywheel, to store energy.

When electric power is required from the flywheel battery, the H-bridgecontrols regenerative braking current by switching Q4 at PWM frequencyfor one back-emf polarity, and Q3 for the opposite. D1 injects currentpulses from node 5 into node 4 while D3 free-wheels for the firstpolarity, D2 and D4 for the opposite. This operating mode deceleratesthe flywheel, to recover electric power. Power switches Q1, Q2, Q3, andQ4 are preferably semiconductors with good switching characteristics,such as MOSFETs or IGBTs. Diodes D1, D2, D3, and D4 are preferablyfast-recovery soft-turnoff rectifiers. MOSFETs have intrinsic diodes;some have adequate reverse recovery attributes to be used for thisfree-wheeling function. Capacitor C has low loss for high-frequencycurrent. It stores and supplies PWM current pulses.

H-bridge 34 is controlled by PWM driver 33, which is responsive tovarious input commands, including the feedback signals from the rotorangle sensors. Flywheel rotational speed increase can be inhibited by avibration discriminator responsive to signals in the axial and radialservos, after processing to determine if axial or radial excursions orrate persist beyond a prescribed time. Dc buss voltage can be regulatedas needed by negative voltage feedback from the buss.

Although it requires added inductors, this type of motor/generatorfacilitates use of ferrite inductor cores having far lower losses ininductors essential to PWM current control. In the prior art that usessalient-pole laminated-iron-core motor/generators, much higher motorcore loss is sustained under PWM drive. Also, with that prior art,permanent magnets from a spinning rotor magnetically cycle the statoriron, causing high idling loss due to magnetic hysteresis. In a vacuumenclosure, these losses cause heating, which is not easily transferredaway from hot components of a flywheel assembly. Also, the inner rotorpermanent magnets of the prior art require high-strength annular bandsaround them, to prevent their disintegration from centrifugal forces.These bands increase gap length and decrease radial clearance betweenthe rotor and stator. They also increase cost.

Unlike conventional stator windings in slots, with magnetic fields thatlink them practically confined to their surrounding iron core so thateach conductor reacts with the same flux, the motor/generator of thisinvention has a magnetic field which is not uniform at the statorwindings. This also has caused high eddy losses in the prior art, asexplained below:

If solid magnet wire stator windings are used, they are subjected tomagnetic fields that are not uniform over their relatively largecross-sections. This is illustrated by points 7 a and 7 r, which are ina magnetic field having a sinusoidal variation with angle (summed overactive winding length) around the spin axis that sweeps by these points.It is also illustrated by points 7 i and 7 o, which are in a magneticfield that is not radially uniform.

Differences in axial EMF induced at 7 a and 7 r, and 7 i and 7 o, arethus responsible for eddy currents flowing in concentric eddy loopsalong the entire two rotor lengths of winding 7 in the rotating magneticfield produced by a spinning rotor. The wide dashed line in FIG. 3aillustrates the eddy current path in a representative segment of statorconductor 7. Insulation 7 x is shown at each side of thiscross-sectional view. The eddy currents do not produce useful power orenergy conversion, because they do not exert net torque, and do notproduce back-emf across the stator terminals. They dissipate energy andcause heating in the stator windings.

Eddy loss in winding 71, at the moment of relative rotor position shownin FIG. 3, is considerably higher than in winding 7, because fieldgradient is maximum when crossing through zero (i.e., between themagnets).

Stranded magnet wire can reduce eddy loss substantially. By way ofexplanation, if points 7 a and 7 r, and 7 i and 7 o, representcross-sections of very small diameter copper wire strands, eachindividually insulated from the others by an insulating coating,localized eddy current is prevented unless it flows through therespective winding terminals 7 c and 7 e where the strands connect.Insulation around each strand blocks eddy current that would otherwisecirculate within a large diameter conductor in the rotor field.

For a stator winding wherein individual insulated strands are notspiraled, and straight active conductors are disposed as shown in FIG.3, EMF generated along a rotor length of strand 7 a on one side of thespin-axis will ideally equal EMF generated across strand 7 r on theother side. And if, at the bottom of the stator (in the inactive windingsegment between the two straight active segments in the rotor field)each strand is interchanged radially about the center of the group, sothat 7 i and 7 o appear as shown at each side of the spin-axis,different EMFs generated over the length of each strand will likewisehave equal sums, connected across 7 c and 7 e. Minimizing loss due todifference current between conductor strands, with these straight activeconductors, requires experimentation and consistent carefulwire-forming.

This example of eddy bucking (i.e., EMF equalizing over the length ofeach strand, to prevent difference current flow though one strand thatcontinues through any another, and thus circulating in an equivalenteddy manner through the group of strands) is predicated on symmetric andopposite radial magnetic field strength along a plane passing throughthe spin axis. Insofar as a part of the sinusoidal flux varies almostlinearly across the bundle of strands, the summed EMFs presented at thewinding terminals, of each individual strand, disposed in between thoseshown (7 a, 7 r, 7 i, and 7 o), are also equal.

Ideally, effective blocking and bucking (by terminal-to-terminalincremental emf summing that cancels total back-emf differences alongeach strand's total length) can be achieved by equalizing differencesthat would otherwise cause eddy currents and their power dissipation.

In production wire forming procedures, maintaining the relativepositions of each strand, as set forth herein, requires very specializedtooling. Stranded wire is intentionally spiraled to improve formingqualities, like bending compliance and ability to keep strands in agroup. If a slight amount of spiral is not well defined, strandpositions may inadvertently be interchanged when formed, from one sideto the other. This could cause eddy current losses in strandedconductors, that is comparable to that of eddy loss in solidlarge-diameter windings.

An easier method to buck and block eddy currents, and yet have thebenefits of more compliant forming quality inherent in spiraled strandedwire, is to use a spiral pitch wherein the emf sum of each strand isequalized over several segments within the stator winding length. Thismethod is consistent with the long spindle length set forth herein, toachieve other benefits described above. However, each strand is longer,and consequently has higher resistance, with close spiral twisting. Butproduction costs may be far less than the parallel strand example, whosebenefit from shorter conductor length may be overshadowed by formingdifficulty. The examples used here explain, with a sequence of windingoptions, the principles involved. Spiraled, insulated-strand statorwindings are one preferred embodiment of this invention. The straight,insulated-strand windings, formed as set forth here, are another.

Litz wire also achieves eddy loss reduction. But it is far moreexpensive than insulated-strand magnet wire, and is bulkier for the sameterminal-to-terminal resistance. Insulated-strand copper wire, commonlyknown as magnet wire, is less expensive, takes less space, and so makesbetter use of rotor magnets. Litz wire was developed to reduce lossesfrom high-frequency skin effect, wherein required current through theconductor flows mainly along the surface of large diameter conductors,due to more high-frequency inductive coupling near the center, whichrestricts current there. It basically reduces conductive area, byforcing more current to flow where inductance is less (i.e., near theconductor skin).

Eddy loss has commonly been confused with skin effect in the priorcoreless motor/generator art, particularly when used in flywheelbatteries, where idling loss is so detrimental. But idling loss issurely not caused by skin effect, mainly because skin effect restrictseffective (i.e., required) current through conductors. Clearly, requiredstator current is zero during motor/generator idling.

Skin effect may lower motor/generator power conversion efficiency asmall amount: A 2-pole rotor spinning at 100,000 rpm which has requiredstator current at an electrical frequency of 1667 cycles per second,will conduct most of the current through its skin depth of 0.064 inch.That means that even a 0.125 inch diameter copper conductor will be ableto conduct current through most of its cross-sectional area. Litz wiremay utilize its small diameter strands a bit more, but their total areawill be less, and length will be more, than solid or stranded wire. SoLitz wire in flywheel battery motor/generators can reduce eddy loss, butwill generally have more resistance to stator current, compared to theindividually insulated multi-strand conductors set forth herein.

Basic equations defining operation of the 2-phase 2-pole motor/generatoras set forth in the present invention are, for one stator phase:

Back-emf (volts)=0.67×10⁻⁸×{number turns per phase}×{stator diameter(inches)}×{field strength (gauss)}×{stator height (inches)}×{rotorrpm}×{sin (rotor angle)}

Torque (inch pounds)=56×10⁻⁸×{number turns per phase}×{stator diameter(inches)}×{field strength (gauss)}×{stator height (inches)}×{peakcurrent (amperes)}×{sin² (rotor angle)}

For the other phase, sine terms are replaced by cosine. So the sum oftorque from the two phases is proportional to sin² (rotor angle)+cos²(rotor angle) which will have negligible ripple with reasonably goodsinusoidal rotor field distribution. The PWM power electronics sumscurrent through the two phases in accordance with the same relationship,and thereby exchanges current with the dc power buss, which likewise hasnegligible ripple. All polyphase configurations perform this type ofcomplementary summing, albeit with more terms than this simpler 2-phaseexample.

A preferred embodiment of the axial levitation servo loop is shown inconventional block diagram form, by FIG. 5, a representation well knownin the feedback control system art.

Block 35 denotes gain with limiting (especially to prevent excessivenegative demagnetizing fields) and a small dead-band (to reduceexcessive response to small perturbations), 36 is gain, and 37 denotes asumming operation wherever shown here. Block 38 represents the transferfunction for a PWM H-bridge and coil 18. The PWM H-bridge here isidentical to the one illustrated in FIG. 4, and coil 18 is physicallyshown in both FIG. 2 and FIG. 11. In block 38, L_(c) represents the coilinductance and R_(c) its resistance. Wherever shown here in a transferfunction, s denotes the Laplace operator. Block 36 provides currentfeedback gain to shorten time lag due to inductance L_(c).

Transfer function k_(m), which varies as a complex function of rotorassembly position z, also depends on properties of annular,axially-magnetized, permanent-magnet 16, which is physically illustratedin FIG. 2. Rate feedback 50 is denoted by transfer function k_(d)s, andis derived from the axial position sensor 53 denoted by its incrementalmotion sensitivity k_(z).

Force from gravity 51 on the rotor assembly, is proportional to itsweight 52 denoted by its mass M. Block 49 denotes integrator transferfunction k_(i)/s, whose output will drive the feedback loop until therotor assembly is axially positioned where axial force due to themagnetic field from permanent magnet 16, with current in coil 18 equalto zero, is equal to the rotor assembly weight. Block 49 output ispreferably limited intrinsically (shown by 35 a) in accordance withlevels to accommodate magnet property tolerances, and is capable of bothpositive and negative axial position adjustment. Maximum output from 35a is less than the maximum output from 53, so that position feedbackalways determines nominal axial position, with the integrator onlyadjusting it. Integration can be implemented by analog circuits, or byan up/down counter, depending mainly on production quantity.

Dynamic analysis computer programs can accurately determine stabilityand response of this servo loop, and can help greatly to optimize it; incombination with a finite element analysis program to accuratelycharacterize magnetostatic fields and forces of elements shown withinthe dashed rectangle that is labeled “Magnetics.”

For example, physical dimensions and properties of coil 18, injuxtaposition with permanent magnet 16 and related annular magneticmaterials, would be entered, to determine flux densities B nearby,especially in the gap between their poles, and how axial force F_(m)varies with incremental position z for a given nominal position. This isthen entered into the dynamics analysis to test responsiveness andstability at various positions.

FIG. 6 shows a simplified servo block diagram for two diametricallyopposite radial electromagnets and associated electronics.Electromagnets at the top of the rotor assembly are represented by 20and 21, and their radial position sensor by 22, as in FIG. 2.Diametrically opposite electromagnets are represented as 20 _(o) and 21_(o). Transfer functions of their respective coils are designated 60 and60 _(o). Their associated servo electronics are designated by transferfunctions 63, 64, and 65. Electromagnets at the bottom (80 and 81,opposite 80 _(o) and 81 _(o), and their sensor 24) are controlled bylike servo loops.

Transfer functions B/I and B/I_(o) for respective opposite coils 20 and20 _(o) denote flux density B vs. coil current I (and I_(o)). Blocks 60and 60 _(o) denote the transfer function l/(sL+R) of voltage applied toand current through respective radial electromagnet coils. Blocks 21 and21 _(o) denote respective actuator force F_(x) vs. flux density B at agiven nominal position x. Block 62 denotes the dynamic relation of forceF_(x), rotor assembly mass M (with actuators assumed equidistant fromits center of gravity), time, and motion x. Block 24 denotes radialsensor 24 sensitivity k_(x), block 63 is rate feedback k_(d)s, and block64 is feedback gain.

Zero-crossover dead-band is denoted by block 65, wherein feedback signalv_(in) results in v_(out)=0 for prescribed small deviations fromgeometric center. A polarity discriminator drives a corresponding PWMcircuit, with effective value v_(out), if the polarity is true for thatoutput. Otherwise, the coil current free-wheels through a diode. Coilcurrents I and I_(o) are sensed internal to the servo loop electronics;and are subjected to the indicated polarity test therein.

Axial and radial position sensors can be implemented by Hall-effect ormagnetoresistive magnetic field sensors, or by capacitive, inductive, orelectro-optical means, known in the prior art. Hall-effect andmagnetoresistive methods require an isolated magnetic source near therotor assembly, and possible magnetic shielding or separation bydistance from stray magnetic fields. Inductive sensing uses rotor steelto complete magnetic paths, and thereby affect inductance of coilslinked thereto. It is relatively immune to stray flux, and stable overcontinued long use, but requires generally more excitation power; andthe cooperative rotor steel incurs continuous hysteresis loss.Electro-optic sensing uses a set of light-emitting-diodes andphoto-diodes. It is immune to stray magnetic fields. Althoughlight-emitting-diode efficiency decreases somewhat over time, theresulting loop gain reduction does not seriously affect loop dynamics.Capacitive sensing uses the distance between a conductive ring on therotor assembly, to fixed electrodes juxtaposed therewith, to provide aradial position signal that is also immune to stray flux.

A capacitive axial and radial position sensor is set forth here, withreference to FIG. 12; wherein U1, R1, and C2 provide an essentiallysquare-wave excitation at nominally 12 volts peak-to-peak, at a nominal2 megahertz frequency. For axial position sensing, this excitationvoltage is applied to fixed conducting exciter ring 53 e, which isjuxtaposed and near rotatable conducting ring 53 r. The rotatable ringis attached to an insulator segment of the rotor assembly, relativelydistant from other conductive material (especially components that mightsubject it and fixed conductive sensor ring 53 s to electromagneticinterference). This arrangement detects axial position, primarily bycapacitance between 53 s and 53 r, and secondarily by capacitancebetween 53 e and 53 r. This series capacitance is nominally severalpicofarads, and varies a few picofarads, with axial movement z fromnominal position z_(n). Capacitance between these adjacent fixed androtating conductors can be computed from:

C={8.85×10⁻¹² (farad/meter)}{Area (meter²)}/{Separation (meters)}

which can be combined with:

I={volts peak-to-peak}{frequency}{C}

to yield rectified sensor output current:

I _(z) ={V _(DD)}{excitation frequency}{C _(n)/(1−z/z _(n))}

where C_(n) is nominal effective series capacitance between 53 e and 53r, and 53 r to 53 s (and accounts for a small stray capacitance between53 r to ground), z is axial movement, and z_(n) is nominal axial spacingbetween the fixed and rotatable rings.

The rectified signal is filtered by C3 and amplified by operationalamplifier circuit U2, whose midband gain is (R4+R6)/R4. C4 provides ratefeedback for the axial servo. C5 and R5 provide high frequency gainroll-off. R3 provides an output level adjustment. To minimize straycapacitance and signal corruption, this part of the axial servoelectronics is located near fixed ring 53 s. Faraday shields, tomaintain signal integrity, are connected to circuit ground.

Rotatable conductive cylinder 22 r is similarly attached to an insulatorsegment of the rotor assembly. It is capacitively coupled to excitationat a frequency of over 2 megahertz via fixed exciter cylinder 22 e.Radial motion x is sensed by diametrically opposite, fixed electrodes 22s and 22 so. They provide respective rectified signals:

I _(x) ={V _(DD)}{frequency}{C _(n)/(1+x/x _(n))} and I _(xo) ={V_(DD)}{frequency}{C _(n)/(1−x/x _(n))}

These radial position signals are likewise amplified, by operationalamplifier circuits U3 and U4, which likewise provide rate feedback andhigh-frequency roll-off. Respective U3 and U4 outputs are applied todifferential amplifiers U5 and U6. Dead-band is set by R7 and R8. Whendead-band is exceeded in one direction, U5 provides an output. Whendead-band is exceeded in the opposite direction, U6 alternativelyprovides a like output. These signals are applied to respective PWMdrivers 90 and 91, which control respective radial electromagnets 20 and20 _(o) through PWM power switches Q5 and Q6.

Sensor electrodes to detect radial motion 90° from that sensed by 22 sand 22 so are shown without associated radial servo circuits in FIG. 12between 22 s and 22 so. Circuits which complete the radial servoscontrolling radial electromagnets aligned with these electrodes, areidentical to those shown with 22 s and 22 so. A preferred embodimentincludes four upper electromagnets with corresponding sensor electrodesand radial servos, plus four lower electromagnets with like electrodesand servo circuits. They are preferably packaged within the flywheelenclosure, with U3, U4, and the other six low-signal-level circuitspackaged in close proximity to their respective sensor electrodes. Thenumber of hermetic feed-throughs is thus minimized, by including allparts of the radial servos within the flywheel enclosure.

Another axial and radial position sensor embodiment includes magneticmeans. It is illustrated in FIG. 13, which shows a partial cross-sectionthrough the spin-axis, at a high-permeability section 11 of the rotorassembly. It includes one pair of sensors, 153 s and 153 so, 180° apart,to provide axial position feedback. Axial magnetic field B at thesensors varies with gap S_(g) between 11 and fixed annular iron poles153 and 153 i, according to the approximate expression:

B=B _(r)(1+2S _(g) /w _(m))

where B_(r) is flux density at zero gap (known as magnet remanence orretentivity), and w_(m) is {magnet radial width}{magnet axialwidth}/{pole width}. Flux is provided by annular magnet 153 m, which isradially magnetized. Signals from 153 s and 153 so are summed by anoperational amplifier circuit, to provide axial position feedback forthe axial servo. Summing accommodates any lack of perpendicularity,between the spin axis and the surface of rotor assembly segment 11adjacent to these sensors, or possible wobble, that might otherwisecause unwanted axial servo response and consequent energy dissipation.

Radial position sensing is provided by a pair of diametrically opposedmagnetic sensors, 24 s+ and 24 s−, plus a like pair disposed 90° fromthem, which are not shown in this view. These sensors provide radialposition signals, which vary inversely with the gaps at respectivesensors, between 11 and fixed annular iron poles 24 and 24 i. Radialmagnetic fields are provided in these gaps by annular magnet 24 m, whichis axially magnetized. Flux varies at each sensor, likewise according tothe expression B=B_(r)/(1+2S_(g)/w_(m)) where S_(g) is the gap at aparticular radial sensor. Note that if the gap increases at one sensor,the gap decreases at the diametrically opposite sensor. Signals from 24s+ and 24 s− are applied to a differential amplifier. This compensatesfor possible magnetic strength variation, that would otherwise causecentering error. Forces from the radial magnetic fields needed bymagnetic radial position sensors are not negligible, and their inherentinstability must be compensated by the axial magnetics and radialelectromagnets. Ferromagnetic annular steel poles accommodate low costmagnets, by providing a uniform field in the gap regions, despitepossible magnet defects, chips, cracks, and lack of uniform magneticstrength. This circumvents magnetic cycling of rotor assembly iron 11,which might otherwise cause idling loss. Unstable radial forces, between11 and the fixed magnetic materials 24, 24 i and 24 m, can be smallcompared to nominal radial forces of the magnetic bearing, with smalllow-intensity magnetic sensor components. Note that the outer diameterof rotor iron 11 extends beyond that of 153; this circumvents axialsensor sensitivity to radial motion.

Both the capacitive and magnetic position sensors set forth above have anon-linear response to rotor assembly position. Gain at small gaps canbe several times higher than at large gaps. This complicates servo loopstability. But it affords an inherent opportunity to have magneticbearings that stiffen during large excursions from nominal positions, indirections approaching possibly destructive contact between the rotorassembly and adjacent stationary parts.

Yet another axial and radial magnetic sensor embodiment is illustratedby FIG. 14, which likewise shows a partial cross-section through therotor spin axis. It obtains both axial and radial position signals fromthe same pair of sensors 153 s and 153 so, plus a pair disposed 90° fromthese, which is not shown in this view. Note that the outercircumference of 11 reaches only to the middle of the sensors. Outputsfrom all four sensors, in response to axial motion, vary substantiallytogether. Outputs from respective sensors 180° apart, in response toradial motion parallel to a line between them, vary in opposition toeach other (i.e., one output decreases while the other increases). Tothe extent that radial excursions of 11 are small, the amount one outputdecreases will equal the amount which the opposite output increases.Thus the sum of the outputs, and their rate of change, should not varysignificantly from such radial excursions. With this sum fed to theother components of the axial servo, any sensitivity to radialexcursions (herein termed cross-talk) would interfere with the axialservo loop. Likewise, any differences in respective sensor outputs,arising from axial excursions, would interfere with the radial servoloops. Such cross-talk does not significantly degrade magnetic bearingperformance, during normal operation, for the stationary vertical-axisflywheel battery installations of this invention.

Accordingly, the four sensor outputs of FIG. 14 are summed, to provideaxial position feedback for the axial servo. For the radial servos,sensor outputs from each pair are fed to corresponding operationalamplifier circuits, which derive rate by a configuration essentiallyidentical to that described for the capacitive sensors illustrated byFIG. 12. Output from the operational amplifiers of FIG. 14 is likewiseapplied to two differential amplifiers, which cancel signal componentsdue to axial motion and add dead-band. Their outputs are fed to theradial servo circuits, which control a pair of opposing radialelectromagnets. These components are essentially identical to thosedescribed in more detail for the capacitive position sensors illustratedin FIG. 12. However, the FIG. 14 embodiment results in axial and radialposition sensors having far higher cross-talk, between axial and radialservos, compared to FIG. 12 and FIG. 13. Nevertheless, it needs lessparts (except for servo circuits, which are the same), and will thuscost less. And need to circumvent radial force instability of the FIG.14 embodiment, is considerably less than that of FIG. 13.

Capacitive axial and radial position sensing, from four sensors, 90°apart, similar to 22 s and 22 so shown in FIG. 12, is analogous to thatof the magnetic sensors in FIG. 14. The rotatable conductor 22 r wouldneed to have a conical form near the sensors, and the sensors would needto be accordingly inclined, to achieve requisite axial sensitivity.However, servo circuits remain the same as those in FIG. 12, cost iscomparable, and cross-talk is far more troublesome. So separatecapacitive sensors, as in FIG. 12, are preferred for this invention.

An alternate embodiment, of the axial and radial position sensors,includes the capacitive radial sensors shown in FIG. 12 near the top ofthe rotor assembly, plus the magnetic axial and radial sensors shown inFIG. 14 near the bottom. This takes advantage of the lighter weightcapacitive sensors at the top, and their immunity to stray magneticfields (which are higher near the top). By placing the heavier,iron-dependent, magnetic sensors near the bottom, a lowercenter-of-gravity is facilitated, and their susceptibility to straymagnetic fields is not so troublesome, because stray magnetic fields areminimal near the bottom of the rotor assembly. Nevertheless, capacitiveposition sensing (with its negligible forces) is preferred overmagnetic.

High and sustained electromagnet activity, excluding that required todamp normally slight vibration at certain resonant frequencies, mayindicate incipient rim failure. It may also indicate effects of abnormalseismic activity. In either case, discriminators having over-ridecontrol of electronics which control the motor/generator and backupbearings, can inhibit motor/generator drive whenever any of the servodrive levels exceed a prescribed maximum over a prescribed timeinterval, to help prevent flywheel damage and possible explosion.

It will be appreciated that the motor/generator and integral magneticbearings of this invention would also provide benefits, in addition tothose described herein for flywheel batteries, to other applications.

One such application would be as a vertical-spin-axis turn-table for alarge data storage and retrieval system, where continuous and reliableoperation is crucial. If data is stored on magnetic media, it isexpected that magnetic shielding may be added, so that the strong fieldsneeded for motor and magnetic bearing functions do not contaminate data.Another use would be as an integral vertical-spin-axis high-speed pumpor turbine, for fluids or gases that are incompatible with conventionalmechanical bearing lubricants.

Flywheel battery backup bearings (23, 23 a, 25, and 25 a in FIG. 2) willengage only when the flywheel is not in service, or upon possibleelectronics failure or disconnect as described above, to restrict axialand radial flywheel motion and so avoid flywheel damage.

Clearance between the rotor spindle and backup bearing contact surfacesshould be smaller than distances between a nominally centered rotorassembly and any other stationary part. When the flywheel assembly is incontact with either the upper or lower backup bearing, pressure on thecontact surfaces is mainly due to the rotor assembly weight minus liftfrom the axial levitation means, plus abnormal external acceleration.Cushioning provided by an annular spring, preferably on the rotorspindle, can absorb shock and reduce impact forces. Contact surfaces,that accommodate rotor spin by sliding, preferably have large contactareas, to reduce contact pressure and to provide high thermalconduction, in a direct and large area path as is practical, to theflywheel enclosure. The most simple and lowest cost embodiment of theinvention has journal backup bearings with beveled sliding contactsurfaces, such as 23 and 25. They limit axial and radial flywheelexcursions, and do not include ball bearings 23 a and 25 a, the motors26 and 28, nor their drive mechanisms (such as element 27), shown inFIG. 2.

Rolling contact bearings, with rolling separators between ball or rollerbearings, instead of conventional sliding retainers (also known ascages), and instead of journal bearings with sliding load-bearingsurfaces, would depend far less upon lubrication. However, they are notwidely manufactured and distributed, mainly due to manufacturingdifficulties.

According to the prior art, rolling contact bearings confrontmanufacturing problems, due to difficult assembly and need for closedimensional tolerance. Improvements to circumvent these problems are setforth herein with reference to FIG. 7 and FIG. 8.

These improvements should facilitate production assembly processes,permit less stringent dimensional tolerances, and provide rollingcontact between load-bearing balls and separators that is notintermittent. It also permits rolling separators and related elements ofthis invention to be substituted directly for sliding cages ofconventional ball bearings.

FIG. 7 illustrates a cross-sectional view, through its spin-axis, of apreferred embodiment of the improved rolling contact mechanical bearing.FIG. 8 illustrates an axial cross-sectional view, in a planeperpendicular to the spin-axis, of the improved bearing.

Conventional inner bearing race 40 has an inner diameter intended forstandard shaft attachment. Its outer diameter has an annular grooverecess to provide a raceway for a plurality of ball bearings 41 eachhaving equal radii smaller than the curvature of the raceway, to remaincentered with the raceway and maintain essentially point contact whilerolling thereon.

Outer bearing race 39 likewise provides a rolling surface for the ballbearings. Separator rollers 42 are interposed between each ball, tomaintain equal spacing between balls and prevent scraping betweenotherwise adjacent surfaces which move in opposite directions. Theseparator rollers spin in rolling contact with the balls. The separatorsare necked at their axial centers, with a neck radius larger than theball radius, to remain centered axially and to maintain essentiallypoint contact while rolling therewith, along a contact circumference ofthe separator at its center.

The separators are restrained from moving radially outward of thebearing axis by outer idler race 43, which provides a rolling surfacethat makes contact with the separator along a recessed neckcircumference centered therewith. The separators are restrained frommoving inward by inner idler race 44, which makes rolling contact withthe same recessed neck circumference.

Kinematic analysis shows that, if the separators are located along thesame bolt circle as the center of each ball, and that if the separatorneck in contact with the balls has the same diameter as the neck incontact with the idlers, inner idler race 44 will not rotate relative tothe bearing outer race.

Likewise, if the separator centers are each located on straight linesconnecting the centers of adjacent balls, and the separator neck incontact with the idlers is equal to the neck in contact with the ballsmultiplied by the factor cos(180°/(number of balls)), the inner idlerrace will not rotate relative to the bearing outer race.

The inner idler race diameter would then equal:

{inner bearing race diameter+ball diameter} {cos(180°/(number ofballs))}−{separator neck diameter contacting the idlers}.

And the outer idler race diameter would equal:

{inner idler race diameter}+(2){separator neck diameter contacting theidlers}.

This is the preferred embodiment, because there is no outward thrust onthe separators due to contact with the balls, and ball separation can bemaintained with minimum contact forces between the balls and theseparators. Insofar as the inner bearing race spins, separator skew willtend to be corrected by gyroscopic precession torque, acting on theseparators at their high spin rates. Separator precession is zero whenits spin axis is parallel to the bearing spin axis.

Since the inner idler race does not need to rotate relative to the outerbearing race, it can be in contact with cover 45, which is affixed tothe outer bearing race. Cover 45 is preferably a metal and is radiallyrigid to stiffen the inner idler. Its radial stiffness permits the inneridler to be a relatively thin, radially compliant and elastic ring, tofacilitate its assembly with the separators, outer idler, and ballbearings.

To further facilitate assembly, the inner idler can be made even morecompliant radially, by having equally spaced axial grooves in its innercircumference, spaced to have several grooves distributed evenly withinan angle of 360°/(number of balls). Mechanized assembly is therebyfacilitated, that is far easier and less costly than assembly of rollingcontact bearings of the prior art. Added parts and processes willincrease cost only slightly over conventional ball bearings.

Hollow thin-wall separators fabricated from annealed spring steel tubingthat is then necked by a metal spinning process, then heat treated toextend its elastic deformation range, allows the separators to be moreeasily assembled with the ball bearing while maintaining a zero or verysmall clearance for the assembly. Solid materials used in the prior artrequire much closer dimensional control, and do not facilitate practicalassembly of separators designed for zero or very small clearance fit.

The outer idler race spins at a high speed, and therefore is subjectedto centrifugal forces due to its own mass. The hollow thin-wallseparators that it also supports against centrifugal forces will subjectouter idlers to forces lower than heavier solid members used in theprior art.

Another advantage of thin-wall separators, fabricated from materialoperating well within its elastic limit, is their low strain in thisseparator implementation. Both these factors combine to result inextremely low rolling loss from mechanical hysteresis. Metals arepreferable to plastic, which has lower thermal conductivity and willoutgas far more than metals. Plastic also has high rolling loss due tomechanical hysteresis. Local heat buildup can be destructive if backupbearings are engaged in the event of a prolonged abnormal condition,with the flywheel spinning at maximum speed. The idler races and coveron the opposite side of the bearing illustrated in FIG. 7 can beidentical to those described above.

It will be appreciated that the rolling contact bearings of the presentinvention would also have advantages for other applications. Suchapplications include all low-loss bearings, to support rotatable shafts,for uses and environments not compatible with bearing lubricants.

Lower cost would be facilitated, by backup bearings having slidingsurfaces, provided only by beveled contact surfaces 23 and 25 exceptthey would preferably be broader than illustrated in FIG. 2, at the topand bottom of the rotor assembly. Increased surface area would result inlower contact pressure and higher thermal conductivity where heat isgenerated. Also, in this embodiment, non-rotating parts of the backupbearing would be affixed to the enclosure by material with high thermalconductivity so as to provide maximum heat transfer.

With zero maintenance and long life, which should result from theimprovements provided by this invention, underground installation wouldbe practical. The flywheel assembly enclosure is preferably mounted with2-axis gimbals (90° apart) supporting it from its top, the gimbals on astand supported by the base of a frangible rigid liner, resting onleveled sand fill.

The gimbals constrain the enclosure so that it does not rotate due toreaction from stator torque, and inherently maintain the enclosureverticality by gravity alone. Thus, verticality will be maintained, evenif the sand or the earth below it were to shift from its initialleveling. The stand and liner base will preferably have protrusions,which prevent turning, which could otherwise result from torque betweenthe motor/generator rotor and stator, or between a possibledisintegrating flywheel and its enclosure.

The preferred flywheel enclosure installation site is in a cylindricalhole prepared for this purpose. The hole will preferably be dug in aconstruction area planned to be covered by a reinforced concrete slabfloor, for a parking or storage area, prior to pouring concrete for thatarea's floor. Backfill is then poured into the cylindrical hole, andcompacted to support the liner, which protects and maintains a cleanspace for the flywheel enclosure, and conduit connecting it towall-mounted associated electronics, in the area constructed above thefloor.

The liner also facilitates installation of far more costly items (likethe flywheel in its enclosure) at a later date, when they can beprotected from vandalism, theft, and inadvertent damage from buildingconstruction activity. Backfill can then be poured around the liner, andthe concrete slab floor poured above it, around an annular insert havinga removable (with special tools) steel cover plate fastened thereto.

The backfill is preferably a porous sand mixture, which is readilyavailable at construction sites, is low cost, is not flammable, notdegradable, and can absorb an explosive blast without a high pressurereflected shock wave. The concrete slab, and the cover plate over theflywheel enclosure, should provide an effective barrier, to protectpeople in and around the building, and prevent damage to the building inthe event of a possible exploding flywheel.

Associated electronics, connected to the flywheel enclosure by anelectrical conduit having protective metal armor around it, ispreferably housed in a single wall-mounted cabinet. This providesconvenient access for viewing its data monitor at the cabinet front, andfor setting command variables like startup, shutdown, time-of-day powerstorage, power-down, and possible power schedules for discretionaryloads. It also provides a clear air flow path, to cool electronics inthe cabinet.

Installed as set forth hereabove, the flywheel enclosure need not becapable of containing a possible flywheel explosion. The enclosure ispreferably constructed of light thin-wall metal, such as aluminum,mainly because it will outgas far less than many other materials, can befabricated to high precision tolerances, and can withstand possiblebumping and scraping during assembly and handling procedures withoutdamaging its structural or interior vacuum integrity. A preferredembodiment will contain absorptive and adsorptive getters in theenclosure, to help maintain its interior vacuum. A small vacuum pump,responsive to a vacuum sensor or to idling loss, can be added, toautomatically prevent long-term vacuum loss.

It will be appreciated that this invention may have many othervariations in addition to those described by example herein, withappropriate embodiments of constituent elements herein described to bestsuit a particular situation. Accordingly, it is intended that the claimsas set forth hereinafter cover all such applications, embodiments, andvariations thereto within the true spirit and scope of this invention.

I claim as new and a significant improvement to the prior art, anddesire to secure by Letters Patent:
 1. A flywheel battery, for storingelectric power as kinetic energy from a dc power buss and returningpower to said buss with minimal losses, comprising: motor/generatormeans, including polyphase stator windings for conducting polyphasesinusoidal currents, which are formed from multi-strand insulatedconductors for eddy blocking and bucking, a permanent-magnet rotor forproviding radial flux that interacts with said currents, and rotor anglesensors, for providing polyphase feedback signals which vary essentiallysinusoidally with rotor angle; a flywheel rim, for providing rotaryinertia for storing said kinetic energy, attached to saidmotor/generator rotor and concentric therewith, the combination having avertical spin axis; power interface electronics, connected to said dcpower buss and to said polyphase stator windings of saidmotor/generator, said electronics responsive to the rotor angle sensorsand to the buss voltage, for controlling polyphase current through saidstator windings so its resultant magnetic field rotates synchronouslywith said rotor, axial servo means, including axial position sensors,also including annular permanent-magnet and magnetic materials forproducing concentric annular poles above the rotor and flywheel, forproviding axial force with minimal magnetic cycling, for levitating therotor and flywheel and for passive radial centering, including aconcentric coil between said poles, its bi-directional currentcontrolled by an axial servo loop responsive to said axial positionsensors, for stabilizing the axial force, including a currentintegrator, for adjusting axial position to reach zero steady-statecurrent; radial servo means, including radial position sensors at therotor top and bottom, including radial electromagnets aligned thereto,for radially centering the rotor by forces from magnetic fields withflux paths substantially radial and axial in cooperating rotor magneticmaterial, controlled by radial servo loops responsive to said radialposition sensors and having dead-band means wherein centering ismaintained by said passive radial centering, gravity, and gyrodynamics.2. The flywheel battery of claim 1, including mechanical backupbearings, near the top and bottom of the rotor and flywheel assembly,and normally not in contact with it, for supporting the rotatableassembly when said axial and radial servo means are not operating, andfurther including: at least one backup bearing actuation motor, forengaging and disengaging the backup bearing contact surfaces andcooperative rotatable mechanical bearing surfaces; a jack-screwmechanism, driven by said actuation motor, for axially positioning saidcontact surfaces.
 3. The flywheel battery of claim 2, further includinga signal discriminator, having vibration discriminator means, responsiveto signals from said axial and radial servo loops, for providingoverride signals to the power interface electronics and drive signals tosaid actuation motor.
 4. The motor/generator of claim 1, including:polyphase stator windings, having multi-strand insulated conductorsformed for blocking and bucking eddy currents therein, embedded in anon-magnetic cylinder affixed to the enclosure, to conduct polyphasecurrents varying sinusoidally with rotor angle so the resulting statorfield is synchronized to rotor angle, for producing torque between therotor and the stator, and for exchanging electric power with the powerinterface electronics while incurring minimal hysteresis and eddylosses; rotor angle sensor means, for providing polyphase feedbacksignals which vary essentially sinusoidally with rotor angle; at leastone pair of rotor magnets, with one magnet of the pair magnetizedradially outward and the other magnetized radially inward, to provideradial flux, which varies essentially sinusoidally with rotor angle,through the stator windings; an outer cylinder of high-permeabilitysteel, for supporting the magnets therein and for providing an outerflux path; an inner cylinder of high-permeability steel, attached to theouter cylinder, for providing an inner flux path, and for completingthrough the stator windings a flux pattern which rotates with the rotor.5. The power interface electronics of claim 1, comprising: signalprocessing means, responsive to the rotor angle sensors, the dc powerbuss voltage, and to input commands, for controlling PWM H-bridges; PWMH-bridges, responsive to the signal processing means, connected, withparallel capacitors, across the dc power buss, and through series outputinductors to respective stator windings, for controlling sinusoidalpolyphase currents through the stator windings, and for exchanging dccurrent with the dc power buss.
 6. The axial servo means of claim 1,comprising: a fixed annular permanent-magnet, a high-permeabilityannular inner pole, and a high-permeability annular outer pole, abovethe rotor and flywheel, to provide an axial magnetic field uniform withrotor angle in an annular gap region, for levitating and passivelycentering the rotor and flywheel; a fixed annular concentric coilaffixed to the permanent-magnet and high-permeability poles, foradjusting and stabilizing the magnetic field in the annular gap region;rotatable annular high-permeability poles, attached to the rotor andflywheel near its top, and juxtaposed beneath the fixed poles andconcentric coil, to provide axial lift and passive radial centeringforces, for the rotor and flywheel; axial position sensors, fordetecting the rotor and flywheel assembly axial position; axial servoloop means, responsive to the axial position sensors, for controllingcurrent through the concentric coil, to stabilize and adjust axialposition of the rotor and flywheel; integrator means, responsive to theconcentric coil current, for adjusting axial position of the rotor andflywheel, so that longterm coil current is reduced to nearly zero. 7.The axial servo means of claim 1, including: a fixed annularpermanent-magnet, a high-permeability annular inner pole, and ahigh-permeability annular outer pole with outer diameter at the pole gapsmaller than the outer diameter of the permanent-magnet, above the rotorand flywheel, to provide a concentrated axial magnetic field uniformwith rotor angle in an annular gap region, for levitating and passivelycentering the rotor and flywheel; a fixed annular concentric coil,affixed to the permanent-magnet and high-permeability poles, foradjusting and stabilizing the magnetic field in the annular gap region;rotatable annular high-permeability poles, attached to the rotor andflywheel near its top, and juxtaposed beneath the fixed poles andconcentric coil to provide axial lift and passive radial centeringforces, for the rotor and flywheel; axial position sensors, fordetecting the rotor and flywheel assembly axial position; axial servoloop means, responsive to the axial position sensors, for controllingcurrent through the concentric coil, to stabilize and adjust axialposition of the rotor and flywheel; integrator means, responsive to theconcentric coil current, for adjusting axial position of the rotor andflywheel, so that long-term coil current is reduced to nearly zero. 8.The radial servo means of claim 1, including: at least three radialelectromagnets near the top, and at least three near the bottom, of therotor and flywheel assembly, fixed to the flywheel enclosure, eachincluding a coil around high-permeability steel, its two poles injuxtaposition with the rotor to conduct a magnetic field having asubstantially radial and axial path in the rotor, for providing radialattraction forces between the electromagnets and cooperating cylindricalhigh-permeability steel attached to and coaxial with the rotor andflywheel, with minimal flux cycling in the cooperating magneticmaterials; at least two radial position sensors near the top, and atleast two near the bottom, of the rotor and flywheel assembly; radialservo loops, responsive to the radial position sensors, for controllingcurrent through the coils of the radial electromagnets; dead-band means,for inhibiting said current when the flywheel assembly spin-axis iscentered within tolerance and rate of radial motion is less than aprescribed level, to maintain spin-axis centering and verticality duringnormal operation, by said passive radial centering, gravity, andgyrodynamics.
 9. Mechanical backup bearings as in claim 2, each alsocomprising: a ball bearing having a fixed outer race and a rotatableinner race, and a plurality of load-bearing balls therebetween, whichroll in contact with the inner and outer race; separators between eachof the balls, formed from thin-wall tubing of a spring material, eachhaving a neck at its center to maintain axial centering and rollingcontact with two balls, and having necks near both of its ends forrolling contact with idler races; outer idler races at both sides of thebearing, to provide outer raceways for the necks of each separator neartheir respective ends; inner idler races at both sides of the bearing,to provide inner raceways for the necks of each separator near theirrespective ends; a cover at each side of the bearing, each having aradially rigid inner shoulder to radially stiffen the adjoining inneridler race; means for affixing the covers to the outer race of the ballbearing.
 10. The polyphase stator windings in claim 1, each comprising:a group of conductor strands, each insulated from the other, formed intheir inactive region between their two straight axial active segments,so as to interchange strands about the group center, to equalize,between winding terminal connections, back-emf of each strand.
 11. Thepolyphase stator windings in claim 1, each comprising: a group ofconductor stands, each insulated from the others between windingterminal connections, the group spiraled, to equalize, between windingterminal connections, back-emf of each strand.
 12. The axial positionsensor in claim 1, comprising: high-frequency oscillator means, tosupply an excitation voltage; a fixed conductive exciter ring, connectedto the excitation voltage; a rotatable conductive ring, attached to therotor assembly by means of an insulating annular member and having asurface capacitively coupled to the exciter ring; a fixed conductivesensor ring, capacitively coupled to the rotatable ring, for providing asignal responsive to capacitance between the sensor ring and rotatablering; current rectifier and filter means, for removing thehigh-frequency component from the signal provided by the sensor ring;operational amplifier means, for providing feedback to the axial servomeans, responsive to the rotor assembly axial position and excursionrate.
 13. The radial position sensors in claim 1, each comprising:high-frequency oscillator means, to supply an excitation voltage; afixed conductive exciter cylinder, connected to the excitation voltage;a rotatable conductive cylinder, attached to the rotor assembly by meansof an insulating annular member, and having a surface capacitivelycoupled to the exciter cylinder; four fixed sensor electrodes, 90°apart, capacitively coupled to the rotatable cylinder, for providing twosignal pairs, responsive to capacitances between opposing electrodes andthe rotatable cylinder, current rectifier and filter means, connected torespective sensor electrodes, for removing the high-frequency componentfrom signals provided by the sensor electrodes; operational amplifiermeans, for providing two amplified signal pairs, responsive to the rotorassembly radial position and excursion rate; differential amplifiermeans, for providing pairs of outputs, with dead-band, to respectiveradial servos, proportional to the difference between said amplifiedsignal pairs.
 14. The axial position sensor of claim 1, comprising:fixed annular permanent magnet means, with affixed inner and outerhigh-permeability annular poles, for providing an axial magnetic field;a rotatable high-permeability annular section of the rotor assembly,having a flat shoulder near the annular poles, to complete a path forthe magnetic field varying with axial position; a pair of magneticintensity sensors 180° apart, affixed to one annular pole, for providinga pair of sensor outputs responsive to the axial magnetic field in thegap between the annular pole and the rotatable annular section;operational amplifier means, for providing feedback to the axial servo,proportional to the sum of the sensor outputs plus their rates ofchange.
 15. The radial position sensors of claim 1, each comprising:fixed annular permanent magnet means, with affixed upper and lowerhigh-permeability annular poles, for providing a radial magnetic field;a rotatable high-permeability annular section of the rotor assembly,having an outer surface near the annular poles, to complete a path forthe magnetic field; four magnetic intensity sensors, 90° apart, affixedto one annular pole in the gap between the pole and the rotatableannular section, and each providing an output signal responsive to theradial magnetic field at its respective location; operational amplifiermeans, for providing two signal output pairs, which vary with oppositemagnetic sensor output amplitude and rate of change; differentialamplifier means, for providing pairs of outputs, with dead-band, torespective radial servos, proportional to the difference between thesignal output pairs.
 16. The motor/generator of claim 1, including:polyphase stator windings, having multi-strand insulated conductorsformed for blocking and bucking eddy currents therein, embedded in anon-magnetic cylinder affixed to the enclosure, to conduct polyphasecurrents varying sinusoidally with rotor angle so the resulting statorfield is synchronized to rotor angle, for producing torque between therotor and the stator, and for exchanging electric power with the powerinterface electronics while incurring minimal hysteresis and eddylosses; at least one pair of rotor magnets, with one magnet of the pairmagnetized radially outward and the other magnetized radially inward, toprovide radial flux, which varies essentially sinusoidally with rotorangle, through the stator windings; rotor angle sensor means, responsiveto said radial flux, for providing polyphase feedback signals which varyessentially sinusoidally with rotor angle; an outer cylinder ofhigh-permeability steel, for supporting the magnets therein and forproviding an outer flux path; an inner cylinder of high-permeabilitysteel, attached to the outer cylinder, for providing an inner flux path,and for completing through the stator windings a flux pattern whichrotates with the rotor.
 17. The motor/generator of claim 1, including:polyphase stator windings, having multi-strand insulated conductorsformed for blocking and bucking eddy currents therein, embedded in anon-magnetic cylinder affixed to the enclosure, to conduct polyphasecurrents varying sinusoidally with rotor angle so the resulting statorfield is synchronized to rotor angle, for producing torque between therotor and the stator, and for exchanging electric power with the powerinterface electronics while incurring minimal hysteresis and eddylosses; rotor angle sensor means, for providing polyphase feedbacksignals which vary essentially sinusoidally with rotor angle; at leastone pair of a rotor magnet group each composed of three magnets, whereinthe middle magnet of the group is stronger than the other two, with onegroup magnetized radially outward and the other group magnetizedradially inward, to provide radial flux, which varies essentiallysinusoidally with rotor angle, through the stator windings; an outercylinder of high-permeability steel, for supporting the magnets thereinand for providing an outer flux path; an inner cylinder ofhigh-permeability steel, attached to the outer cylinder, for providingan inner flux path, and for completing through the stator windings aflux pattern which rotates with the rotor.
 18. The flywheel battery ofclaim 1, further including a vacuum enclosure, containing therein saidmotor/generator, flywheel rim, and axial and radial servo means, andhaving hermetic connections to power interface electronics outside theenclosure.
 19. The flywheel battery of claim 3, further including avacuum enclosure, containing therein said motor/generator, flywheel rim,axial and radial servo means, mechanical backup bearings, and havinghermetic connections to power interface electronics outside theenclosure.
 20. A flywheel battery, for storing electric power as kineticenergy from a dc power buss and returning power to said buss withminimal losses, comprising: power interface electronics, connected tosaid buss and to polyphase stator windings of a motor/generator, saidelectronics responsive to rotor angle sensors, to the buss voltage, andto override signals from a signal discriminator, for controllingpolyphase current through said stator windings so its resultant magneticfield rotates synchronously with said rotor, a flywheel rim, attached tosaid rotor and coaxial therewith, having a vertical spin axis, forproviding rotary inertia for storing said kinetic energy; saidmotor/generator, for converting power with minimal magnetic cycling ofmagnetic materials and minimal eddy losses in conductors, havingpolyphase stator windings formed from multi-strand insulated conductorsfor eddy blocking and bucking, a permanent-magnet rotor for providingradial flux, and said rotor angle sensors, for providing polyphasefeedback signals which vary essentially sinusoidally with rotor angle;axial servo means, responsive to axial position sensors, includingannular permanent-magnet and magnetic materials for producing concentricannular poles above the rotor and flywheel for providing axial forcewith minimal magnetic cycling, for levitating the rotor and flywheel andfor passive radial centering, including a concentric coil between saidpoles, its bidirectional current controlled by an axial servo loop, forstabilizing the axial force, including a current integrator, foradjusting axial position to reach zero steady-state current; radialservo means, responsive to radial position sensors at the rotor top andbottom, including radial electromagnets aligned thereto, for radiallycentering the rotor by forces from magnetic fields with flux pathssubstantially radial and axial in the rotor, controlled by radial servoloops having deadband means wherein centering is maintained by saidpassive radial centering, gravity, and gyrodynamics; said signaldiscriminator, including vibration discriminator means, responsive tosignals from said axial and radial servo loops, for providing overridesignals to the power interface electronics; mechanical backup bearings,near the top and bottom of the rotor, and normally not in contact withit, for supporting the rotor when said axial and radial servo means arenot operating; a vacuum enclosure, containing therein saidmotor/generator, flywheel rim, axial and radial servo means, andmechanical backup bearings, and having hermetic connections to powerinterface electronics outside the enclosure.
 21. The power interfaceelectronics in claim 20, comprising: signal processing means, responsiveto the rotor angle sensors, the dc power buss voltage, to the vibrationdiscriminator, and to input commands, for controlling PWM H-bridges; PWMH-bridges, responsive to the signal processing means, connected, withparallel capacitors, across the dc power buss, and through series outputinductors to respective stator windings, for controlling sinusoidalpolyphase currents through the stator windings, and for exchanging dccurrent with the dc power buss.
 22. The motor/generator of claim 20,including: polyphase stator windings, having multi-strand insulatedconductors formed for blocking and bucking eddy currents therein,embedded in a non-magnetic cylinder affixed to the enclosure, to conductpolyphase currents varying sinusoidally with rotor angle so theresulting stator field is synchronized to rotor angle, for producingtorque between the rotor and the stator, and for exchanging electricpower with the power interface electronics while incurring minimalhysteresis and eddy losses; rotor angle sensor means, for providingpolyphase feedback signals which vary essentially sinusoidally withrotor angle; at least one pair of rotor magnets, with one magnet of thepair magnetized radially outward and the other magnetized radiallyinward, to provide radial flux, which varies essentially sinusoidallywith rotor angle, through the stator windings; an outer cylinder ofhigh-permeability steel, for supporting the magnets therein and forproviding an outer flux path; an inner cylinder of high-permeabilitysteel, attached to the outer cylinder, for providing an inner flux path,and for completing through the stator windings a flux pattern whichrotates with the rotor.
 23. The axial servo means in claim 20,comprising: a fixed annular permanent-magnet, with high-permeabilityannular steel poles, above the rotor and flywheel, within and supportedby the vacuum enclosure, to provide an axial magnetic field uniform withrotor angle in an annular gap region, for levitating the rotor andflywheel; a fixed, annular, concentric coil, affixed to thepermanent-magnet and steel poles, for adjusting and stabilizing themagnetic field in the annular gap region; rotatable annularhigh-permeability steel poles, attached to the rotor and flywheel nearits top, and juxtaposed beneath the fixed permanent-magnet, poles, andconcentric coil, to provide axial lift and radial centering forces, forthe rotor and flywheel; axial position sensors, for detecting the rotorand flywheel assembly axial position; axial servo means, responsive tothe axial position sensors, for controlling current through theconcentric coil, to stabilize and adjust axial position of the rotor andflywheel; integrator means, responsive to the concentric coil current,for adjusting axial position of the rotor and flywheel, so thatlong-term coil current is reduced to nearly zero.
 24. The radial servomeans of claim 20, including: at least three radial electromagnets nearthe top, and at least three near the bottom, of the rotor and flywheelassembly, fixed to the flywheel enclosure, each including a coil aroundhigh-permeability steel, its two poles in juxtaposition with the rotorto conduct a magnetic field having a substantially radial and axial pathin the rotor, for providing radial attraction forces between theelectromagnets and cooperating cylindrical high-permeability steelattached to and coaxial with the rotor and flywheel, with minimal fluxcycling in the cooperating magnetic materials; at least two radialposition sensors near the top, and at least two near the bottom, of therotor and flywheel assembly; radial servo loops, responsive to theradial position sensors, for controlling current through the coils ofthe radial electromagnets; dead-band means, for inhibiting said currentwhen the flywheel assembly spin-axis is centered within tolerance andrate of radial motion is less than a prescribed level, to maintainspin-axis centering and verticality during normal operation, by saidpassive radial centering, gravity, and gyrodynamics.
 25. Mechanicalbackup bearings as in claim 20, each also comprising: a ball bearinghaving a fixed outer race and a rotatable inner race, and a plurality ofload-bearing balls therebetween, which roll in contact with the innerand outer race; separators between each of the balls, formed fromthin-wall tubing of a spring material, each having a neck at its centerto maintain axial centering and rolling contact with two balls, andhaving necks near both of its ends for rolling contact with idler races;outer idler races at both sides of the bearing, to provide outerraceways for the necks of each separator near their respective ends;inner idler races at both sides of the bearing, to provide innerraceways for the necks of each separator near their respective ends; acover at each side of the bearing, each having a radially rigid innershoulder to radially stiffen the adjoining inner idler race; means foraffixing the covers to the outer race of the ball bearing.
 26. Thepolyphase stator windings in claim 22, each comprising: a group ofconductor strands, each insulated from the other, formed in theirinactive region between their two straight axial active segments, so asto interchange strands about the group center, to equalize, betweenwinding terminal connections, back-emf of each strand.
 27. The polyphasestator windings in claim 22, each comprising: a group of conductorstrands, each insulated from the others between winding terminalconnections, the group spiraled, to equalize, between winding terminalconnections, back-emf of each strand.
 28. Vibration discriminator means,as in claim 20, responsive to position and rate signals from the axialservo and the plurality of radial servos, comprising: signal processingmeans, responsive to the servo signals, for providing override signalsto the power interface electronics, for inhibiting speed increase of themotor/generator; an output for providing motor drive, to engage anddisengage the backup bearings.
 29. The axial position sensor in claim20, comprising: high-frequency oscillator means, to supply an excitationvoltage; a fixed conductive exciter ring, connected to the excitationvoltage; a rotatable conductive ring, attached to the rotor assembly bymeans of an insulating annular member and having a source capacitivelycoupled to the exciter ring; a fixed conductive sensor ring,capacitively coupled to the rotatable ring, for providing a signalresponsive to capacitance between the sensor ring and rotatable ring;current rectifier and filter means, for removing the high-frequencycomponent from the signal provided by the sensor ring; operationalamplifier means, for providing feedback to the axial servo, responsiveto the rotor assembly axial position and excursion rate.
 30. The radialposition sensors in claim 20, each comprising: high-frequency oscillatormeans, to supply an excitation voltage; a fixed conductive excitercylinder, connected to the excitation voltage; a rotatable conductivecylinder, attached to the rotor assembly by means of an insulatingannular member, and having a surface capacitively coupled to the excitercylinder; four fixed sensor electrodes, 90° apart, capacitively coupledto the rotatable cylinder, for providing two signal pairs, responsive tocapacitances between opposing electrodes and the rotatable cylinder;current rectifier and filter means, connected to respective sensorelectrodes, for removing the high-frequency component from signalsprovided by the sensor electrodes; operational amplifier means, forproviding two amplified signal pairs, responsive to the rotor assemblyradial position and excursion rate; differential amplifier mean, forproviding pairs of outputs, with dead-band, to respective radial servos,proportional to the difference between said amplified signal pairs. 31.The axial position sensor in claim 20, comprising: fixed annularpermanent magnet means, with affixed inner and outer high-permeabilityannular poles, for providing an axial magnetic field; a rotatablehigh-permeability annular section of the rotor assembly, having a flatshoulder near the annular poles, to complete a path for the magneticfield varying with axial position; a pair of magnetic intensity sensors180° apart, affixed to one annular pole, for providing a pair of sensoroutputs responsive to the axial magnetic field in the gap between theannular pole and the rotatable annular section; operational amplifiermeans, for providing feedback to the axial servo, proportional to thesum of the sensor outputs plus their rates of change.
 32. The radialposition sensors in claim 20, each comprising: fixed annular permanentmagnet means, with affixed upper and lower high-permeability annularpoles, for providing a radial magnetic field; a rotatablehigh-permeability annular section of the rotor assembly, having an outersurface near the annular poles, to complete a path for the magneticfield; four magnetic intensity sensors, 90° apart, affixed to oneannular pole in the gap between the pole and the rotatable annularsection, and each providing an output signal responsive to the radialmagnetic field at its respective location; operational amplifier means,for providing two signal output pairs, which vary with opposite magneticsensor output amplitude and rate of change; differential amplifiermeans, for providing pairs of outputs, with dead-band, to respectiveradial servos, proportional to the difference between the signal outputpairs.
 33. Combined axial and radial position sensors as in claim 20,comprising: fixed annular permanent magnet means, with affixed inner andouter high-permeability annular poles, for providing a magnetic field; arotatable high-permeability annular section of the rotor assembly,having a flat shoulder of diameter approximately equal to the distancebetween a pair of magnetic sensors, to complete a path for the magneticfield which varies with axial and radial rotor position; four magneticsensors, 90° apart, affixed to the outer annular pole, for providingoutputs responsive to the magnetic field in the gap between the outerpole and the rotatable annular section; operational amplifier means, forproviding feedback to the axial servo, proportional to the sum of thesensor outputs plus their rates of change; operational amplifiercircuits, for providing signals proportional to respective sensoroutputs and rates of change; differential amplifier means, responsive tosaid signals, for providing outputs, with dead-band, to correspondingradial servos, proportional to differences between paired signals. 34.Mechanical backup bearings as in claim 20, each also comprising: a ballbearing having a fixed outer race and a rotatable inner race, and aplurality of load-bearing balls therebetween, which roll in contact withthe inner and outer race; separators between each of the balls, formedfrom thin-wall tubing of a spring material, each having a neck at itscenter to maintain rolling contact with two balls, and having necks nearboth of its ends for maintaining rolling contact with idler races; outeridler races at both sides of the bearing, to provide outer raceways forthe necks of each separator near their respective ends; inner idlerraces at both sides of the bearing, to provide inner raceways for thenecks of each separator near their respective ends; a cover at each sideof the bearing each having a radially rigid inner shoulder to stiffenthe adjoining inner idler race; means for affixing the covers to theouter race of the ball bearing.
 35. The axial servo means of claim 20,including: a fixed annular permanent-magnet, a high-permeability annularinner pole, and a high-permeability annular outer pole with outerdiameter at the pole gap smaller than the outer diameter of thepermanent-magnet, above the rotor and flywheel, to provide aconcentrated axial magnetic field uniform with rotor angle in an annulargap region, for levitating and passively centering the rotor andflywheel; a fixed annular concentric coil, affixed to thepermanent-magnet and high-permeability poles, for adjusting andstabilizing the magnetic field in the annular gap region; rotatableannular high-permeability poles, attached to the rotor and flywheel nearits top, and juxtaposed beneath the fixed poles and concentric coil, toprovide axial lift and passive radial centering forces, for the rotorand flywheel; axial position sensors, for detecting the rotor andflywheel assembly axial position; axial servo loop means, responsive tothe axial position sensors, for controlling current through theconcentric coil, to stabilize and adjust axial position of the rotor andflywheel; integrator means, responsive to the concentric coil current,for adjusting axial position of the rotor and flywheel, so thatlong-term coil current is reduced to nearly zero.
 36. Themotor/generator of claim 20, including: polyphase stator windings,having multi-strand insulated conductors formed for blocking and buckingeddy currents therein, embedded in a non-magnetic cylinder affixed tothe enclosure, to conduct polyphase currents varying sinusoidally withrotor angle so the resulting stator field is synchronized to rotorangle, for producing torque between the rotor and the stator, and forexchanging electric power with the power interface electronics whileincurring minimal hysteresis and eddy losses; at least one pair of rotormagnets, with one magnet of the pair magnetized radially outward and theother magnetized radially inward, to provide radial flux, which variesessentially sinusoidally with rotor angle, through the stator windings;rotor angle sensor means, responsive to said radial flux, for providingpolyphase feedback signals which vary essentially sinusoidally withrotor angle; an outer cylinder of high-permeability steel, forsupporting the magnets therein and for providing an outer flux path; aninner cylinder of high-permeability steel, attached to the outercylinder, for providing an inner flux path, and for completing throughthe stator windings a flux pattern which rotates with the rotor.
 37. Themotor/generator of claim 20, including: polyphase stator windings,having multi-strand insulated conductors formed for blocking and buckingeddy currents therein, embedded in a non-magnetic cylinder affixed tothe enclosure, to conduct polyphase currents varying sinusoidally withrotor angle so the resulting stator field is synchronized to rotorangle, for producing torque between the rotor and the stator, and forexchanging electric power with the power interface electronics whileincurring minimal hysteresis and eddy losses; rotor angle sensor means,for providing polyphase feedback signals which vary essentiallysinusoidally with rotor angle; at least one pair of a rotor magnet groupeach composed of three magnets, wherein the middle magnet of the groupis stronger than the other two, with one group magnetized radiallyoutward and the other group magnetized radially inward, to provideradial flux, which varies essentially sinusoidally with rotor angle,through the stator windings; an outer cylinder of high-permeabilitysteel, for supporting the magnets therein and for providing an outerflux path; an inner cylinder of high-permeability steel, attached to theouter cylinder, for providing an inner flux path, and for completingthrough the stator windings a flux pattern which rotates with the rotor.38. The motor/generator of claim 20, including: polyphase statorwindings, having multi-strand insulated conductors formed for blockingand bucking eddy currents therein, embedded in a non-magnetic cylinderaffixed to the enclosure, to conduct polyphase currents varyingsinusoidally with rotor angle so the resulting stator field issynchronized to rotor angle, for producing torque between the rotor andthe stator, and for exchanging electric power with the power interfaceelectronics while incurring minimal hysteresis and eddy losses; at leastone pair of a rotor magnet group each composed of three magnets, whereinthe middle magnet of the group is stronger than the other two, with onegroup magnetized radially outward and the other group magnetizedradially inward, to provide radial flux, which varies essentiallysinusoidally with rotor angle, through the stator windings; rotor anglesensor means, responsive to said radial flux, for providing polyphasefeedback signals which vary essentially sinusoidally with rotor angle;an outer cylinder of high-permeability steel for supporting the magnetstherein and for providing an outer flux path; an inner cylinder ofhigh-permeability steel, attached to the outer cylinder, for providingan inner flux path, and for completing through the stator windings aflux pattern which rotates with the rotor.